Coating for metallic articles



' objects of aluminum.

Patented Dec. 16, 1941 rd a. Carney, Miami, Fla.

'No Drawing. Application April 18, 1939, Serial No. 268,644

'2 Claims. (01. 621(l8.5)

This invention relates to methods of treating aluminum and likesurfaces, and more particularlyto improved methods of providing afinish-- ing andprotective coating upon the external surfaces ofaluminum ice trays 'and grids or other In order to obtain protectivecoatings on aluminum surfaces it has been customary in the past to makethe aluminum object to be coated the anode in an electrolytic cellhaving a solution of sulphuric acid as the electrolyte. The resultantcoating is a surface layer which is very porous, of varying" thicknessand varying hardness characteristics. When used for the manufacturing ofgrids or trays or similar objects the coating is washed and then thepores are sealed by the use of oils, waxes, lacquers or the like. Thiselectrolytic treatment, the separate washing and sealing operationsinvolve a relatively high cost of processing.

It is accordinglyan important object of the present invention to providea protective coating for aluminum surfaces which is highly resistant tocorrosion and which is readily applied by a simple and relati elyinexpensive coating operation.

A further object of the invention is to provide a finishing coating foraluminum surfaces which has a satiny finish very similar to that of ananodic coating.

A further. object of the invention is to provide a protective coatingfor the above stated purpose whichconsists of a hard tough film of highgloss and which will readily fill the hills and valleys and pores ofthemetal surfaces treated and produce a thoroughly smooth surfaced product.

Other objects and advantages of this invention will appear in thefollowing description and appended claims. Before explaining in detailthe present invention it is to be understood that the phraseology orterminology employed herein is for the purpose of description and not oflimitation, and it is, not intended to limit the invention beyondtherequirements of the prior art.

In accordance with the present invention coatingsof the type describedabove are prepared by first subjecting the object to be coated, for ex-vample an aluminum ice tray or grid, to an etching treatment employingany suitable etching medium such as an acid or 'basic. etching agent as,for example, sulphuric or hydrochloric acid or caustic soda. The etchedobject is'then finished by spraying the object with a urea resin bakingenamel, and then subjecting the object thus coated to temperatures inthe neighborhood of 300 F. in a baking oven to fuse and finally hardenthe coating. .4

In a preferred embodiment of the invention the urea resin baking enamelmay contain the following ingredients in the following approximateproportions:

Parts by weight Urea 60 Formaldehyde (37% strength) 321 Glycerol phtbai'e 60, Butyl alcohol 222 Such a coating is converted from its fluidform to a solid form by a polymerization of the resin under theinfluence of heat. The finish is a hard, clear finish which hassuflicient strength and flexibility to withstand the strains to which itis subjected in use and is highly resistant to corrosion.

The finish effectively ,seals the pores in the metal surfaces which havebeen opened by the g. action of the etching medium and thus, when thefinish is used on the surfaces of objects" such as ice trays and grids,the coating prevents the penetration of water in the exposed pores andurea resin enamel as used herein.

face which is exceedingly smooth and glossy and otherwise attractive.Although the method used to prepare the coatings involves a baking aswell as a coating step, it is readily seen that the meth- .od is verysimple and decidedly less expensive than the methods employed inanodizing metal Moreover, the baking assists in providobjects.

- ing a coating which is'toug'her'and more resistant to abrasion.

It. is to be understood that other coating methods may be employed toapply the enamel, such as dipping or the like, although the use ofspraying methods is preferred. Also any suitable device or method ofbaking may be utilized, provided the temperature can be readilymaintained at about 300 F. p

The methods of the present invention may also be applied to unetchedsurfaces, yet it has been found that a more satisfactory appearance isobtained when the objects being treated are first cleaned and preparedfor the coating step by means of an etching operation. In .some instanceit is advantageous to anodize as well as etch, the metal prior toapplying the enamel, although such combined treatments are usually to beavoided due to the increased cost. 7

Where the object being coated is an ice tray or other article which isexposed to cold or freezing temperatures, it is frequently desirable tosupplement the enamel coating with a thin coating of wax which not onlyadds to the appearance of the tray but permits easier removal of its icecontents by mechanical appliances. An .improved method of applying suchcoating, using wax in the form of a powder, is described in my copendingapplication filed simultaneously with the present application.

Although the invention has been described as applying primarily to thetreatment of ice trays and grids and similar equipment, it may beemployed with equal success in connection with other aluminum objectssuch as the interior shells I of refrigerators and various partsemployed in the automobile and aeronautical industries.

I claim: Y

1. An aluminum tray and grid for receiving water to be frozen, said trayand grid possessing on their respectiv water contacting surfaces awater-repellant adherent relatively flexible protective coating, saidcoating comprising a baked enamel-like layer containing glycerolphthalate and the condensation product of approximately 60 parts byweight of urea and 320 parts by weight of formaldehyde.

2. An aluminum tray. and grid for receiving water to be frozen, saidtray and grid possessing on their respective water contacting surfaces awater-repellant adherent relatively flexible protective coating, saidcoating consisting of the baked enamel-like reaction product ofapproximately 60 parts by weight of urea, approximately 320 parts byweight of 37% formaldehyde, ap-

proximately parts by weight -of glycerol phthalate, and approximately220 parts by weight of butyl alcohol. Y

CLIFFORD R. CARNEY.

